Exposure to poison ivy and poison oak can cause rashes and skin eruptions. Use homeopathic remedies for poison ivy symptoms. Poison oak (Toxicodendron diversilobum) is mostly found on the west coast of the United States, whereas poison ivy (Toxicodendron radican) grows mainly in the east. The leaves of both plants are easy to identify but hard to avoid. They grow in every area of the United States, except in the desert and at high altitudes. Poison ivy grows in Canada and Northern Mexico as well. The name of the oil that causes the reaction is urushiol. The rash is an allergic reaction to the oil and some people are more reactive than others, or not at all.